Electrical interstage control

ABSTRACT

Auxiliary SCR&#39;&#39;s of low current carrying capacity utilized for controlling main SCR&#39;&#39;s of high current carrying capacity, to compensate for internal heating of the main SCR&#39;&#39;s, and physically and spatially separated to compensate for ambient heating.

United States Patent Arthur K. Littwin Lincolnwood, Ill.

[21] App]. No. 608,865

[22] Filed Jan. 12, 1967 [45] Patented Feb. 16, 1971 [73] AssigneesArthur K. Littwin;

Robert L. Littwin; Donald F. Littwin; Horace A. Young, Chicago, Ill. astrustees under trust dated 1/2/51 known as Littwin Family Trust No. l

[72] Inventor [54] ELECTRICAL INTERSTAGE CONTROL 6 Claims, 2 DrawingFigs.

[52] US. Cl 307,252; 307/305 [51] Int. H03k 17/00 [50] Field of Search307/252, 237; 315/251, 192; 328/81; 323/22 (CR), 24

[56] References Cited UNITED STATES PATENTS 3,204,113 8/1965 Snygg315/251 3,299,334 1/ 1967 Ramadah 307/252X 2,666,887 I/ l 954Rockafellow... 315/251 3,181,071 4/1965 Smith et a1 307/252 3,129,3414/1964 Rockafellow 315/251X 3,229,161 l/l966 Anger 315/251X 3,249,8015/1966 Kirk et a1. 3 l 5/251X OTHER REFERENCES G.E. SCR Manual TK2798G491961 Second Edition page 65 Primary Examiner Donald D. Forrer AssistantExaminer-B. P. Davis Attorney-Paul HjGallagher ABSTRACT: Auxiliary SCRsof low current carrying capacity utilized for controlling main SCRs ofhigh current carrying capacity, to compensate for internal heating ofthe main SCRs, and physically and spatially separated to compensate forambient heating.

MAIN CIRCUIT BTI sec- 3g. CONTROL cIRcun' ELECTRICAL INTERSTAGE CONTROLBACKGROUND OF THE INVENTION many installations become heated due to theambient temperatures and for this reason also lose their accuracy ofcontrol.

2. Description of the Prior Art There is no known prior art'relating tothe present invention.

SUMMARY OF THE INVENTION A broad object of the invention is to provide acontrol circuit separate from a main circuit, the control circuitincluding auxiliary SCRs for controlling main SCRs in the main circuitbut arranged to avoid the disadvantageous effects due to heat- Ing.

Another and more specific object is to provide a main circuit and aseparate controlcircuit which is adapted for connection with arelatively low voltage source and not subject to objectionable internalheating, and is out of the effects of the internal heating of the maincircuit, the auxiliary SCRs being utilized to control the main SCRs andto do so without the dis advantages caused by heating of the main SCR's.

I Another and more specific object is to provide a control arrangementof the character just referred to in which the auxiliary SCRstransistors are devoid of the effects of the internal heating of themain SCRs. I

Still another and more specific object is to provide a controlarrangement of the character just referred to in which the auxiliarySCRs are devoid of the effects of ambient heating of the main SCR's.

BRIEF DESCRIPTION OF Tl-IE DRAWING DESCRIPTION OF A PREFERRED EMBODIMENTIn the diagram of FIG. I a main circuit is shown at and a controlcircuit at 12. The main circuit 10 is adapted for connection with arelatively high voltage AC source, and includes line conductors l4, l6and a load 18. The load may be of any of a wide variety of devices,including for example a motor as well as others. In the main circuitalso is a control means indicated generally at 22 in seriestherein, thiscontrol means including a pair of back-to-back main SCRs 24, 26 ofrelatively high current carrying capacity and adapted for accommodatingthe relatively high voltage in the main circuit 10, such as 460 volts,as indicated. Associated with the SCRs are the secondaries 288, 308 oftransformers 28, 30, the primaries of which will be referred tohereinbelow. The secondaries 285, 308 have one terminal connected withthe SCRs and the other with a conductor thereof, forming a circuitthrough the SCR's for performing a gating control thereon, when they areenergized by their primaries as referred to hereinbelow.

The control circuit 12 includes a pair of conductors 32, 34 adapted forconnection with a relatively low voltage AC source, such as l 10 volts,as indicated. Connected across these lines are conductors 36, 38 havingauxiliary SCR's 40, 42 therein, of relatively low current carryingcapacity. These conductors include the primaries 28P, of thetransformers 28, 30, the secondaries I of which are in the circuit 10 asreferred to above. These transformers are of step-up type for providinghigher voltage in the secondaries. The conductors 36, 38 are connectedto a common conductor 44 which is also connected with conductors 46, 48leading from the lines 32, 34 and which have rectifiers 50, 52 therein.The present circuit utilizes back-to-back SCRs and rectifiers, but theinvention is not limited thereto, and may include other arrangementssuch as center tap and bridge networks, etc.

The common conductor 44 leads to a potentiometer 54 from the oppositeside of which leads a conductor 56 having branches 58, 60 leading to thegates of the auxiliary SCR's 40, 42 and, when energized, effective forproducing a gating control on those SCR's. Connected across thepotentiometer 54 is a DC source 62 which may be a battery as indicated,or other instrumentality deriving its energization from the lines 32, 34for example. Connected across the conductors 58, 60 on the one hand andthe common conductor 44 on the other hand, are capacitors 63 and coils648 in series therewith, the coils center tapped to the conductor 44,and forming secondaries of a primary MP of a transformer 64 deriving itsenergization from a suitable source such as conductors 32, 34 as shownat bottom right of FIG. 1.

Upon energizing the circuit 10, and performing a control operation onthe load 18 (or motor 20), it is desired that the power not be appliedat full force constantly, but at varied and cyclically controlledvalues. This is accomplished through the control of the main SCRs 24, 26and specifically by controlling the energization and current carryingcapacity thereof at each cycle of the AC. These SCRs become heated dueto the internal heating effect and also from the ambient temperature inthe instrument in which the load is contained, such for example as in acabinet. The SCR's lose their accuracy in con- 'trol upon becomingheated and the arrangement of the present invention compensates for thatincrease in heat and maintains accuracy of control. The auxiliary SCR's40, 42 are electrically separated from the main SCR's 24, 26 and haveindirect connection therewith through the transformers 28, 30. Therelatively low current carrying capacity auxiliary SCR's 40, 42 do notbecome heated readily, being of little tendency to internal heating andbeing provided with effective heat dissipating means so that theiraccuracy is maintained throughout a wide range of variation insurrounding circumstances. Accordingly, when the auxiliary SCRs 40, 42are energized, they perform a corresponding'energization on the mainSCRs 24, 26 in the manner desired, such for example as either increasingor decreasing the capacity thereof, depending upon the intendedarrangement in their installation. Specifically, in the present instanceupon energization of the auxiliary SCRs 40, 42 the primaries 28P, 30Pare energized which in turn energize the-secondaries 288, 308 in astep-up arrangement, providing greater, voltage and current in thesecondaries with corresponding control functions performed on the mainSCRs 24, 26.

The potentiometer 54 is operative for adjustably setting the SCR's 40,42 so as to control the main SCRs 24, 26 at the desired intervals orportions of the AC cycles. The auxiliary SCRs 40, 42 are gate-controlledfrom the source 62 and when so controlled pass current therethrough,correspondingly energizing the transformers 28, 30. The arrangement ofDC bias provided by the source 62, and the counteracting AC biasprovided by the secondaries 64 produce an unusually accurate control.The DC bias is constantly positive and the AC bias is cyclical andnegative, providing phase angle shift, and by adjusting thepotentiometer, the control of the capacity of the SCRs 40, 42 isinfinitely variable throughout full range. It is desirable that theSCR's not be shut off, but gradually varied, for infinitely varying theaverage gating current in the SCR's 40, 42 and correspondingly varyingthe average current through the SCR's 24, 26. However, the SCRs 40, 42can be completely shut off, or arranged for completely shutting off theSCRs 24, 26, if desired. The arrangement accommodates or compensates.for variations from desired and perfect capacitances, impedances,andrelations therebetween.

FIG. 2 illustrates a physical and spatial separation of the secondarySCRs 40, 42 from the main SCRs 24, 26. In this figure a cabinet orenclosure is indicated diagrammatically at 65 having a pair ofseparate'compartments 66, 68 formed by a central divider 70. These twocompartments are entirely spatially separated from one another by thedivider so that the heat from the SCRs 24, 26, or the transformers,whether from internal heating or from heating through ambienttemperature, is not transmitted to the auxiliary SCRs 40, 42. Theenclosure or cabinet 65 may for example represent a practical structureused in a plant and as such the enclosure tends to confine the heatgenerated. However in the arrangement as represented in FIG. 2, theauxiliary SCRs being in a separate compartment which may beindependently ventilated, are out of the effects of the heat referredto.

While I have herein shown a preferred embodiment of the invention itwill be understood that changes may be made therein within the spiritand scope of the appended claims.

lclaim:

1. Electrical control apparatus for use with an AC source, comprising amain circuit including a load, back-to-back solid state main valve meansin the main circuit, transformers having secondaries controlling thevalve means, a control circuit, back-to-back solid state auxiliary valvemeans in the control circuit, said transformers having primariescontrolled by the auxiliary valve means, the main and auxiliary valvemeans being arranged for mutually counteracting effect responsive torespective phases of the AC, rectifiers respectively associated with theauxiliary valve means and operative for passing current at therespective half cycles of the AC to the associated auxiliary valvemeans, and further including independent variable control means forperforming a gating function on the auxiliary valve means includingconductors to the auxiliary valve means and a common conductor, the lastmeans including a potentiometer connected between the gating conductorsand the common conductor, and further including a supplemental DC sourceacross the potentiometer for controlling the gating of the auxiliaryvalve means.

2. Electrical control apparatus according to claim 1 wherein the meansfor producing the gating current is operative for infinitely varying thecurrent throughout full range, and adapted for adjustment for varyingwithout shutting off the auxiliary control means, or for shutting itoff, selectively.

3. Electrical control apparatus for use with an AC source, a maincircuit including a load, and including main back-toback SCR's andsecondaries of main transformers controlling the gates of those SCRs, acontrol circuit, auxiliary (and) back-to-back SCRs in the controlcircuit in series with the primaries of said transformers, the auxiliarySCR's, through the current passing therethrough and through saidprimaries, controlling the gates in the main SCR's and thereby thecurrent through those SCRs and thus through the load, (second)additional transformers in the control circuit in series with the gatesof the auxiliary SCRs arranged in counteraction to the maintransformers, capacitors in series with the additional transformers, andpotentiometer means operative for controlling the auxiliary SCRsindependently of the (second) additional transformers.

4. Electrical control apparatus according to claim 3 and including a DCsource and the potentiometer means is operative through the DC sourcefor controlling the auxiliary SCR's.

5. Electrical control apparatus for use with an AC source, and includinga pair of conductors including a load, a main control component in oneof the conductors and including back-to-back SCRs, and secondaries oftransformers controlling the gates of those SCR's, a control circuitincluding a pair of conductors adapted for connection with an AC source,the main circuit and control circuit being connected with AC sources ofrelatively greater and lesser voltage, the control circuit including apair of back-to-back auxiliary SCRs connected with the conductors of thecontrol circuit and the primaries of said transformers in series withrespective ones of the auxiliary SCRs, the main and auxiliary SCRs beingarranged for mutual counteraction m respec the we phases 0 AC a commonconductor interconnecting the bases of the auxiliary SCRs, branchconductors connecting the gates of the auxiliary SCRs, additionaltransformers interconnecting said branches and said common conductor,and capacitors in series with respective additional transformers, apotentiometer interconnected between said common conductor and saidbranch conductors and a DC source connected across the potentiometer,the potentiometer being operative for directly controlling the auxiliarySCRs according to the potential output DC independently of the AC, andacting through the gates of the auxiliary SCRs controlling the primariesof said transformers and thereby through the secondaries of those sametransformers controlling the gates of the main SCRs and in turncontrolling the current through the main circuit to the load.

6. Electrical control apparatus according to claim 5 and includingcabinet means having a plurality of compartments heat insulated fromeach other, the main SCR's and said main transformers being in one ofthe compartments, and the auxiliary SCRs being in the other of thecompartments.

1. Electrical control apparatus for use with an AC source, comprising amain circuit including a load, back-to-back solid state main valve meansin the main circuit, transformers having secondaries controlling thevalve means, a control circuit, backto-back solid state auxiliary valvemeans in the control circuit, said transformers having primariescontrolled by the auxiliary valve means, the main and auxiliary valvemeans being arranged for mutually counteracting effect responsive torespective phases of the AC, rectifiers respectively associated with theauxiliary valve means and operative for passing current at therespective half cycles of the AC to the associated auxiliary valvemeans, and further including independent variable control means forperforming a gating function on the auxiliary valve means includingconductors to the auxiliary valve means and a common conductor, the lastmeans including a potentiometer connected between the gating conductorsand the common conductor, and further including a supplemental DC sourceacross the potentiometer for controlling the gating of the auxiliaryvalve means.
 2. Electrical control apparatus according to claim 1wherein the means for producing the gating current is operative forinfinitely varying the current throughout full range, and adapted foradjustment for varying without shutting off the auxiliary control means,or for shutting it off, selectively.
 3. Electrical control apparatus foruse with an AC source, a main circuit including a load, and includingmain back-to-back SCR''s and secondaries of main transfoRmerscontrolling the gates of those SCR''s, a control circuit, auxiliary(and) back-to-back SCR''s in the control circuit in series with theprimaries of said transformers, the auxiliary SCR''s, through thecurrent passing therethrough and through said primaries, controlling thegates in the main SCR''s and thereby the current through those SCR''sand thus through the load, (second) additional transformers in thecontrol circuit in series with the gates of the auxiliary SCR''sarranged in counteraction to the main transformers, capacitors in serieswith the additional transformers, and potentiometer means operative forcontrolling the auxiliary SCR''s independently of the (second)additional transformers.
 4. Electrical control apparatus according toclaim 3 and including a DC source and the potentiometer means isoperative through the DC source for controlling the auxiliary SCR''s. 5.Electrical control apparatus for use with an AC source, and including apair of conductors including a load, a main control component in one ofthe conductors and including back-to-back SCR''s, and secondaries oftransformers controlling the gates of those SCR''s, a control circuitincluding a pair of conductors adapted for connection with an AC source,the main circuit and control circuit being connected with AC sources ofrelatively greater and lesser voltage, the control circuit including apair of back-to-back auxiliary SCR''s connected with the conductors ofthe control circuit and the primaries of said transformers in serieswith respective ones of the auxiliary SCR''s, the main and auxiliarySCR''s being arranged for mutual counteraction in respective phases ofthe AC a common conductor interconnecting the bases of the auxiliarySCR''s, branch conductors connecting the gates of the auxiliary SCR''s,additional transformers interconnecting said branches and said commonconductor, and capacitors in series with respective additionaltransformers, a potentiometer interconnected between said commonconductor and said branch conductors and a DC source connected acrossthe potentiometer, the potentiometer being operative for directlycontrolling the auxiliary SCR''s according to the potential output DCindependently of the AC, and acting through the gates of the auxiliarySCR''s controlling the primaries of said transformers and therebythrough the secondaries of those same transformers controlling the gatesof the main SCR''s and in turn controlling the current through the maincircuit to the load.
 6. Electrical control apparatus according to claim5 and including cabinet means having a plurality of compartments heatinsulated from each other, the main SCR''s and said main transformersbeing in one of the compartments, and the auxiliary SCR''s being in theother of the compartments.